Abberation correction of plurality of beams in color cathode ray tube

ABSTRACT

In a cathode ray tube of the single-gun, plural-beam type in which the plurality of beams are made to intersect each other at a location in the tube between the beam producing means and the screen, a focusing lens for focusing all of the beams on the screen is made up of a plurality of lens components arranged in axial succession and defining an optical center of the focusing lens disposed within the latter, and such focusing lens is positioned so that the optical center thereof is substantially at the location where the beams intersect. The lens components of the focusing lens may be symmetrical or asymmetrical with respect to the optical center, and in the latter case may be effective to compensate for any optical aberrations imparted to certain of the beams when the latter are converged to intersect by means of an auxiliary lens.

ili

Miyaolta ABERATHON CfiRRlECTEON 0F PLURALHTY OF BEAMS 1N COLOR CATHUDIE RAY TUBE lnventor: Senri Miyaoka, Kanagawa-ken, Japan Assignee: Sony Corporation, Tokyo, Japan Filed: June 2, 1969 Appl. No.: 829,421

1F oreign Application Priority Data Apr 23, 1969 Japan ..44/3l398 Apr. 26, 1969 Japan "44/325 46 11.s.c1. .313/70 c, 315/15, 315 13 1111.01. ..H0lj 29/50, 1101 31/20 Field oisearch ..313/69 c, 70c, 92 B;3l5/14,

References Cited UNITED STATES PATENTS 6/1955 Lawrence ..313/70 C X Yoshida et a1. ..3 13/69 C Tretner ..3l3/83 X Primary Examiner-Robert Segal Attorney-Albert C. Johnston, Robert E. Isner, Lewis H. Eslinger and Alvin Sinderbrand In a cathode ray tube of the single-gun, plural-beam type in which the plurality of beams are made to intersect each other at a location in the tube between the beam producing means and the screen, a focusing lens for focusing all of the beams on the screen is made up of a plurality of lens components arranged in axial succession and'defining an optical center of the focusing lens disposed within the latter, and such focusing lens is positioned so that the optical center thereof is substantially at the location where the beams intersect. The lens components of the focusing lens may be symmetrical or asymmetrical with respect to the optical center, and in the latter case may be effective to compensate for any optical aberrations imparted to certain of the beams when the latter are converged to intersect by means of an auxiliary lens.

ABSTRACT 6 Claims, 7 Drawing Figures ABBERATION CORRECTION OF PLURALITY OF BEAMS IN QGILOR CATHOIDE RAY TUBE This invention relates generally to cathode ray or color picture tubes of the single-gun, plural-beam type, an particularly to tubes of that type in which the plural beams are passed substantially through the optical center of a common electron lens by which the beams are focused on the color phosphor screen.

In single-gun, plural beam color picture tubes of the type to which this invention relates, for example, as specifically disclosed in the copending US. application Ser. No. 697,414, filed Jan. 12, 1968 and issuing June 3, 1969 as US. Pat. No. 3,448,316, and having a common assignee herewith, a plurality of electron beams are emitted or originated by a beam generating a cathode assembly and converged to cross or intersect each other at a location between the cathode assembly and the color screen upon which the beams impinge, and a single electron focusing lens for focusing all of the beams on the screen is positioned to dispose its optical center substantially at the location where the beams intersect, whereby the coma and spherical aberrations imparted to the beams by the focusing lens are substantially diminished. When the beams are thus converged to intersect each other substantially at the optical center of the focusing lens, at least certain of the beams emerge from the lens along divergent paths, and pairs of convergence deflecting plates may be arranged along such divergent paths and have voltages applied thereacross to deflect the divergent beams in directions for causing all of the beams to converge at a common point on the apertured beam selecting grill or mask associated with the color screen, or the divergent beams may be allowed to land on the beam selecting grill or mask at spaced locations with suitable time delays being applied to the color signals by which the respective beams are modulated so as to obtain correspondence of the pictures produced on the screen. In either case, the beams are acted upon by the magnetic fields resulting from the application of horizontal and vertical sweep signals to the corresponding coils of a deflection yoke, whereby the beams are made to scan the screen in the desired raster.

in a single-gun, plural-beam color picture tube as described above, the single electron focusing lens must have a sufficiently large power to focus the beams on the screen and thus must correspond to an optically equivalent lens having large curvatures, that is, small radii of curvature at its surfaces, by reason of which the beams, even though passing through the central portion of the single large power electron focusing lens, have some optical aberrations imparted thereto. Further, when the beams are converged to cross or intersect each other substantially at the optical center of the electron focusing lens by means of an auxiliary lens positioned between the beam generating means and the focusing lens, those beams passing through the auxiliary lens at substantial distances from the center of the latter may have some optical aberrations imparted thereto by the auxiliary lens which may be of low power to minimize these aberrations.

Accordingly, it is an object of this invention to provide a cathode ray or color picture tube of the described type in which optical aberrations of the beams, as focused on the color screen, are further minimized.

Another object is to provide a color picture tube of the described type in which any optical aberrations imparted to the beams in consequence of their being converged to intersect at a location between the beam producing means and the screen are fully compensated or corrected in connection with the focusing ofthe beams on the screen.

Still another object is to provide a color picture tube of the described type in which the diametrical size of the beams is limited, at the location of their intersection with each other, so that such beams will impinge on the screen at sharply defined spots.

in accordance with an aspect of this invention, the plural beams of a single-gun, plural beam color picture tube of the described type are focused on the screen by an electron focusing lens made up of a plurality of lens components arranged in axial succession and defining an optical center which is within the focusing lens and disposed substantially at the location where the beams intersect each other. Where the focusing lens is made up of a plurality of lens components, as aforesaid, each of the lens components may be relatively flat or of low power to provide a combined power sufficient to focus the beams on the screen. Further, the lens components disposed before and after the location where the beams intersect each other may impart optical aberrations to the beams that cancel or negate each other, or that completely free the beams of optical aberrations at the screen, even when the beams are made to intersect by means of an auxiliary lens.

It is another feature of this invention to establish an electron lens field for each of the lens components of the focusing lens by means of a plurality of electrodes at different electrical potentials, in which case one of the electrodes is located at the optical center of the focusing lens and has a limiting aperture through which all of the beams pass to constitute a stop for limiting the diametrical size of the beams.

The above, and other objects, features and advantages of the invention, will be apparent in the following detailed description of illustrative embodiments thereof which is to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic sectional view in a horizontal plane passing through the axis of a single-gun, plural-beam color picture tube according to an embodiment of this invention;

FIG. 2 is a view similar to that of FIG. 1, but showing a modification of the color picture tube according to the invention;

FIG. 3 is a fragmentary, schematic sectional view showing another modification of the embodiment of FIG. 1;

FIG. 4 is a view similar to that of FIG. 1, but showing another embodiment of this invention; and

FIGS. 5, 6 and 7 are diagrammatic views illustrating further embodiments of the invention.

Referring to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that a single-gun, plural-beam color picture tube of the type to which this invention is applied may comprise a glass envelope (not shown) having a neck and a cone extending from the neck to a color screen S provided with the usual arrays of color phosphors and with an apertured beam selecting grill AG. Disposed within the neck is a single electron gun having cathodes K K and K each of which is constituted by a beam-generating source with the respective beam-generating surfaces thereof disposed as shown so that the respective beams B B and B emitted therefrom are directed in a substantially horizontal plane containing the axis of the gun, with the central beam B being coincident with such axis and the side beams B and B converging toward the axis. A first grid assembly G of first grids G G and G are spaced from the beam-generating surfaces of cathodes K K and K and have apertures g g and g formed therein in alignment with the respective cathode beam-generating surfaces. A common grid G is spaced from the first grids and has apertures g g and g formed therein in alignment with the respective apertures of the first grids. Successively arranged in the axial direction away from the common grid G are openended, tubular grids or electrodes G G G G and G respectively, with cathodes K K and K grids G, and 6,, and electrodes G G G G and 6, being maintained in the depicted assembled positions thereof, by suitable, nonillustrated support means of an insulating material.

For operation of the electron gun of FIG. 1, appropriate voltages are applied to the grids G, and G and to the electrodes G G G G and G Thus, for example, a voltage ofO to minus 200v. is applied to the grid 6,, a voltage of to 500v. is applied to the grid G a voltage of l0 to 25kv. is applied to the electrodes 0;, G and G and a voltage of 0 to 4kv. is applied to the electrodes G, and G with all of these voltages being based upon the cathode voltage as a reference.

With the applied voltage distribution as described hereinabove, an electron lens field will be established around the axis of electrode G,, by the electrodes G G and G to form a first lens Component Lm, which is indicated in broken lines by its optical equivalent, and an electron lens field will be established around the axis of electrode G by the electrodes G G and G to form a second lens component Lm which is also indicated in broken lines by its optical equivalent. Thus, in accordance with this invention lens components Lm and Lm combine to constitute a main focusing lens Lm having an optical center intermediate lens components Lm and Lm Further, the electrodes G G G G and G constituting main focusing lens Lm are positioned so that the optical center of the latter is disposed substantially at the location where beams B B and B intersect each other.

Also included in the electron gun of FIG. 1 are electron beam convergence deflecting means P which comprise shielding plates P and P disposed in the depicted spaced, relationship at opposite sides of the gun axis, and axially extending, deflector plates Q gnd .QC which are disposed, as shown, in outwardly spaced, opposed relationship to shielding plates P and P, respectively. Although depicted as substantially straight, it is to be understood that the deflector plates Q and Q may, alternatively, be somewhat curved or outwardly bowed, as is well known in the art.

The shielding plates P and P are equally charged and disposed so that the central electron beam B will pass substantially undeflected between the shielding plates P and P, while the deflector plates Q and Q have negative charges with respect to the plates P and P so that respective electron beams B and B will be convergently deflected as shown by the respective passages thereof between the plates P and Q and the plates P and Q. More specifically, a voltage which is equal to the voltage applied to the electrodes G G and 0, may be applied to both shielding plates P and P, and a voltage, which is some 200 to 300v. lower than the voltage applied to plates P and P is applied to the respective deflector plates Q and Q to result in the respective shielding plates P and P being at the same potential, and to result in the application of a deflecting voltage difference or convergence deflecting voltages between the respective plates P and Q and P and Q. It is, of course, this convergence deflecting voltage V which will impart the requisite convergent deflection to the respective electron beams B and B In operation, the respective electron beams B 3,; and B which emanate from the beam generating surfaces of the cathodes K K and K will pass through the respective grid apertures g g and 3 to be intensity modulated with what may be termed the red, green and blue intensity modulation signals applied between the said cathodes and the first grid assembly 6,. The respective electron beams will then be converged by the illustrated positioning of the cathodes to cross each other substantially at the optical center 0 of the main lens L and to emerge from the latter with beams B and B diverging from beam B Thereafter, the central electron beam B will pass substantially undeflected between shielding plates P and P since the latter are at the same potential. Passage of the electron beam 13,, between the plates P and Q and of the electron beam B between the plates P and Q will however, result in the convergent deflections thereof as a result of the convergence deflecting voltage applied therebetween, and the system of FIG. 1 is so arranged that the electron beams B B and B will desirably converge or cross each other at a common spot centered in an aperture g, of the beam selecting grill or mask AG so as to diverge therefrom to strike the respective color phosphors of a corresponding array thereof on screen S. More specifically, it may be noted that the color phosphor screen S is composed ofa large plurality of sets or arrays of vertically extending red, green and blue phosphor stripes or dots S S and S with each of the arrays or sets of color phosphors forming a color picture element. Thus, it will be understood that the common spot of beam convergence corresponds to one of the thusly formed color picture elements.

Electron beam scanning of the face of the color phosphor screen is effected by horizontal and vertical deflection yoke means (not shown) and which receives horizontal and vertical sweep signals whereby a color picture will be provided on the color screen.

With the arrangement shown on FIG. 1, convergence of beams B B and B to intersect each other substantially at optical center 0 is effected by the disposition of the respective beam generating means, so that such convergence is achieved without imparting optical aberrations to any of the beams. In that case, as shown, main focusing lens Lm can be symmetrical about optical center 0, that is, lens components Lm, and Lm are equal and the center 0 is midway therebetween. Since the main focusing lens Lm is made up of the two lens components Lm, and Lm each of these lens components can be of relatively low power and yet have a combined effect sufficient to sharply focus the beams on screen S. The center beam B passes throughthe relatively flat lens components Lm and Lm along their common optical axis, and thus does not have optical aberrations imparted thereto. However, the side beams B and B pass through portions of lens component Lm which are spaced from the optical axis and also through portions of lens component Lm which are spaced from the optical axis. Since beams B and B cross each other or intersect at optical center 0 midway between lens components Lm, and Lm it is apparent that the portions of lens components Lm and Lm through which beam B passes are at opposite sides of the optical axis and, similarly, that the portions of lens components Lm and Lm, through which beam 8,, passes are at opposite sides of the optical axis. Thus, although lens component Lm imparts optical aberrations to beams B and B lens component Lm imparts equal and opposite optical aberrations to these beams, whereby all three beams, at their landing spots on screen S, are free of optical aberrations.

Referring now to FIG. 2, it will be seen that the color picture tube according to the invention as there shown is generally similar to that described above with reference to FIG. 1 and differs therefrom only in that the middle electrode G' of its main focusing lens L'm a plate-like portion in the plane of optical center 0 and provided with a central aperture A through which all of the beams pass at the location of their intersection, whereby aperture A in electrode G' acts as a limiting stop to limit the diametrical size of each of beams B B and B so that the beams impinge on screen S at sharply defined spots. Thus, in the tube of FIG. 2, the three beams are all stopped or diametrically limited by a common stop connected by an electrode of the main focusing lens. However, as shown on FIG. 3, a tube as described above with reference to FIG. 11 may have the electron beams B B and B individually limited or stopped, as by providing the electrode G with limiting apertures g g and g through which the respective beams enter electrode G, of the main focusing lens.

Of course, in accordance with this invention, the number of lens components making up the main focusing lens may be greater than two. Thus, as shown on FIG. 3, the main focusing lens L m of a color picture tube may be constituted by successive, axially arranged electrodes G G,, G G G G and G which are connected, in alternating order, to sources of high and low potentials to establish electron lens fields which form lens components Lm and Lm around the axes of electrodes 6, and G and a third lens component Lm around the axis of electrode G The third lens component Lm is shown midway between lens components Lm, and Lm and, in the case where the latter are equal, the central plane of lens component Lm will contain the optical center 0 of the focusing lens assembly Um at which the intersection of the beams B B and B is substantially located. Thus, as in the embodiment of FIG. 1, any optical aberrations imparted to beams B and B in passing through lens component Lm are fully corrected or compensated for by the opposite and equal aberrations produced by lens component Lm Further, since there are three lens components provided in main focusing lens L m, the necessary focusing power can be achieved with lens components that each have further reduced power, whereby to greatly minimize the optical aberrations imparted to the beams, and particularly to beams B and B in passing through the central lens component Lm along paths at angles to the optical axis. Of course, the arrangement described above with respect to FIG. 3 may be embodied in the color picture tube of FIG. 4 for limiting the diametrical sizes of the beams being focused on the screen.

it will be apparent that the main focusing lens of a color picture tube according to this invention may include more than the three lens components shown on FIG. 4. Thus, as shown diagrammatically on FIG. 5, the main focusing lens L m may consist of four lens components Lm Lm' Lm and Lm with the lens components Lm and Lm' being disposed before the optical center or location of beam intersection and the lens components Lm and Lm being disposed after the center ill, considered in the direction of the beams from the cathodes K K and K to the screen (not shown). So long as the optical aberrations imparted to beams B and B by lens components Lm and Lm' are counteracted or corrected by the equal and opposite optical aberrations imparted by lens components Lm' and Lm such beams will be free of optical aberrations at their landing spots on the screen.

in each of the above described embodiments of the invention, the main focusing lens has been symmetrical, that is, identical lens components have been disposed before and after the optical center or location of intersection of the plural beams. However, as indicated on FIG. 6, a color picture tube according to this invention may have an asymmetrical main focusing lens L m constituted by a lens component Lm, in advance of the intersection 0 of beams B B and B and two lens components llm and lm' disposed after the intersection 0 and which combine to impart to beams B and B optical aberrations which are opposite and equal to the aberrations imparted to such beams by lens component Lm whereby the beams are again free of aberrations at their landing spots on the screen (not shown).

Further, in the foregoing embodiments, the beams B B and B have been converged to intersect at the optical center 0 of the main focusing lens by arranging the beam producing means to emit the beams B and 8,, along paths that converge with respect to the path of center beam B However, as shown on FIG. 7, the present invention can also be applied to color picture tubes in which the beam generating surfaces of 5 cathodes K K and K are disposed in a plane which is substantially perpendicular to the axis of the tube so that the central beam B is emitted coincident with the tube axis and side beams B and B are emitted parallel to the tube axis and at opposite sides of the latter. Further, in this embodiment, the electrode G' has a reduced diameter portion extending into the cupehaped grid G as shown, so that, with the voltage distribution described with reference to FIG. 1, an electron lens field will be established between grid G and electrode G';, to form an auxiliary lens L, as indicated in dashed lines, and by which beams B and 8,, are made to converge to cross or intersect each other and center beam 8 substantially at the optical center 0 of the main focusing lens L m which is constituted by the lens components L m and L m in this case, the main focusing lens L m may be asymmetrical, that is, the lens component L m disposed after the intersection 0 may be made to impart optical aberrations to the side beams B and B that are equal and opposite to the sum of the optical aberrations imparted to such beams by the auxiliary lens L, and by the lens component 1. m, disposed before the intersection 0. Further, in this embodiment, the focusing lens L m may be symmetrical, that is, lens components Um, and L mmay be equal, in which case such lens L m may be positioned with its optical center substantially at, but at a small distance from the location of the intersection of the three beams, whereby to correct for the aberrations of beams B and 8, introduced by the auxiliary or converging lens L Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.

What is claimed is:

l. A cathode ray tube comprising beam-producing means for producing a plurality of electron beams originating at sources that are laterally spaced from each other, a color screen having arrays of different color phosphors which correspond to said beams, apertured beam-selecting means positioned adjacent said screen and having apertures through which said beams pass for impingement on and exciting of the respective phosphors of said arrays, means for directing said beams at angles to each other so as to intersect at a location in said tube between said beam-producing means and said beamselecting means with at least two of said beams following paths that converge to said location from opposed sides of the tube axis and diverge from said location at reversed sides of said tube axis, and means for focusing the electrons of each of said beams on said screen including a plurality of electron focusing lenses arranged in succession along the tube axis and each having a plurality of electrodes at different electrical potentials for establishing a respective electric field by which the beams are focused in passing therethrough, at least one of said electron focusing lenses being disposed between said location where the beams intersect and said beam-producing means and at least another of said electron focusing lenses being disposed between said location and said beam-selecting means so that at least each of said two beams passes through the fields of said one focusing lens and said other focusing lens at distances from, and at opposite sides of said tube axis so as to have opposite aberrations imparted thereto by said one focusing lens and said other focusing for arriving at said screen substantially free of aberrations.

2. A cathode ray tube according to claim 1, in which one of said electrodes is located at said location where the beams intersect and has a limiting aperture through which all of said beams pass to constitute stop means for limiting the diametrical size of the beams.

3. A cathode ray tube according to claim 1, in which said at least one focusing lens and said at least another focusing lens establish identical electric fields which are symmetrically disposed with respect to said location to impart equal and opposite aberrations to at least said two beams.

4. A cathode ray tube according to claim 1, in which there are different numbers of said electron focusing lenses disposed between said location and said beam-producing means and between said location and said beam-selecting means, respectively.

5. A cathode ray tube according to claim 1. in which said means for directing said beams to intersect each other at said location supports said beam sources with the beams issuing therefrom converging to said location.

6. A cathode ray tube according to claim l, in which said means for directing the beams to intersect at said location includes auxiliary lens means disposed between said beamproducing means and said means for focusing the electrons of the beams and causing convergence of said beams to said location, with at least said two beams passing through said auxiliary lens means at regions of the latter spaced from the center thereof so that optical aberrations are imparted to said two beams by said auxiliary lens means, and said at least other focusing lens imparts aberrations to said two beams that are opposite and equal to the aggregate of the aberrations imparted to said two beams by said auxiliary lens means and said at least one focusing lens. 

1. A cathode ray tube comprising beam-producing means for producing a plurality of electron beams originating at sources that are laterally spaced from each other, a color screen having arrays of different color phosphors which correspond to said beams, apertured beam-selecting means positioned adjacent said screen and having apertures through which said beams pass for impingement on and exciting of the respective phosphors of said arrays, means for directing said beams at angles to each other so as to intersect at a location in said tube between said beamproducing means and said beam-selecting means with at least two of said beams following paths that converge to said location from opposed sides of the tube axis and diverge from said location at reversed sides of said tube axis, and means for focusing the electrons of each of said beams on said screen including a plurality of electron focusing lenses arranged in succession along the tube axis and each having a plurality of electrodes at different electrical potentials for establishing a respective electric field by which the beams are focused in passing therethrough, at least one of said electron focusing lenses being disposed between said location where the beams intersect and said beam-producing means and at least another of said electron focusing lenses being disposed between said location and said beam-selecting means so that at least each of said two beams passes through the fields of said one focusing lens and said other focusing lens at distances from, and at opposite sides of said tube axis so as to have opposite aberrations imparted thereto by said one focusing lens and said other focusing for arriving at said screen substantially free of aberrations.
 2. A cathode ray tube according to claim 1, in which one of said electrodes is located at said location where the beams intersect and has a limiting aperture through which all of said beams pass to constitute stop means for limiting the diametrical size of the beams.
 3. A cathode ray tube according to claim 1, in which said at least one focusing lens and said at least another focusing lens establish identical electric fields which are symmetrically disposed with respect to said location to impart equal and opposite aberrations to at least said two beams.
 4. A cathode ray tube according to claim 1, in which there are different numbers of said electron focusing lenses disposed between said location and said beam-producing means and between said location and said beam-selecting means, respectively.
 5. A cathode ray tube according to claim 1, in which said means for directing said beams to intersect each other at said location supports said beam sources with the beams issuing therefrom converging to said location.
 6. A cathode ray tube according to claim 1, in which said means for directing the beams to intersect at said location includes auxiliary lens means disposed between said beam-producing means and said means for focusing the electrons of the beams and causing convergence of said beams to said location, with at least said two beams passing through said auxiliary lens means at regions of the latter spaced from the center thereof so that optical aberrations are imparted to said two beams by said auxiliary lens means, and said at least other focusing lens imparts aberrations to said two beams that are opposite and equal to the aggregate of the aberrations imparted to said two beams by said auxiliary lens means and said at least one focusing lens. 